Obese adolescents are at high risk for later development of non-insulin dependent diabetes (NIDDM) and other metabolic diseases associated with obesity. The objective of this proposal is to implement a school-based intervention program to modify lifestyle in this group to optimize metabolic fitness and reduce the risk of metabolic diseases. We define optimum metabolic fitness as an absence of metabolic and biochemical risk factors associated with obesity, such as glucose intolerance, insulin resistance, hypertension, and hyperlipidemia. The intervention will be implemented through an existing, highly successful school-based clinic located in a racially-mixed high school. The school-based clinic staff, who will assist with the project, are experienced in working with, and are sensitive to, the needs of minority students. We will study two cohorts of obese high school students. In the first cohort, 2 years of intensive intervention will be provided, followed by 1.5 years of participating in a peer tutoring program. In the second cohort, 2 years of intensive intervention alone will be provided. Participants in both cohorts will be obese students at Abraham Lincoln High School (ALHS). Control subjects will be recruited from 2 other high schools having school-based clinics. The 2-year intensive intervention (administered to both cohorts) will involve instruction in nutrition and physical activity, assistance with behavior change, and attention to psychosocial and emotional problems. We will develop a formal curriculum (with major input from participants) which can be incorporated into the general curriculum. Simultaneously, we will work with the food service staff of ALHS to improve the quality of school meals. The physical activity intervention is designed to help students engage in fewer sedentary activities and to develop a love of physical activity. Participants will be exposed to many lifetime activities popular in the Rocky Mountains Region, including hiking, biking and skiing. The effectiveness of the program will be evaluated in terms of sustained changes in behavior, optimization of metabolic fitness, and improvement of psychosocial problems. The focus of the program is not on body weight and participants will be discouraged from frequent evaluations of weight loss. However, significant reductions in body fat content are expected. Finally, the program has been developed so that it can be incorporated permanently into ALHS using existing resources, including the school-based clinic. This will be facilitated by having students and teachers participate in curriculum development. Obese students who require more intensive intervention can receive further help through the school- based clinic. The intervention program we propose can be incorporated into any of the hundreds of schools nationwide which have school-based clinics.